The present invention relates in general to an optical imaging system and more particularly to an optical imaging system useful for projecting images of variable magnification between a fixed object plane and a fixed image plane.
This invention is intended for use in a photocopying environment, though it will be appreciated that its usefulness is not limited to that.
In photocopying machines a light image of the object being copied is projected by means of a lens onto a photosensitive image surface which is then used to make a permanent record of the original object. This is sometimes done by full frame exposure and sometimes by scanning of the original in which a composite image is developed by scanning and projecting incremental portions of the objects. There are numerous ways to perform the scanning function just described. However, it will facilitate an understanding of this invention to describe it in connection with an arrangement in which a moving object is passed over a fixed illuminating apparatus and is imaged on an image member moving synchronously with the moving object. It is to be noted that this aspect of the description is background or environment only and is not a material part of the invention.
In the prior art, image projection systems providing for variable magnification are known and they take several forms. A varifocal or zoom lens between object and image is one known solution. Another is the add-lens arrangement. In yet another type of system, the optical axis between object and image is moved and folded through varying angles to accommodate changes in total conjugate length. In these systems, generally it is necessary to move the imaging lens. Also it is inherent in some such systems that the optical axis is shifted through lateral or angular displacements which must be accommodated.